A key element of high speed, industrial print-on-demand systems is the availability of high speed, highly uniform, patterning devices. One form of patterning device is an electrostatic emitter for ionographic, non-impact printing. The emitter develops a charge pattern on a substrate, e.g., a dielectric drum or plate. The charge pattern is transferred to a print medium and the medium is then coated with a toner powder or liquid that adheres to the charge pattern. The print medium is heated to fix the toner to the medium.
Within the field of electrostatic emitters, the are a wide variety of techniques for charging a substrate in a specific pattern. One common technique for generating charged particles (e.g., ions or electrons) applies a very strong electric field across an air gap, where the air in the gap breaks down to produce ions and electrons. Such an electrostatic emitter is described in U.S. Pat. No. 4,675,703 issued on Jun. 23, 1987 to Richard A. Fotland. Specifically, Fotland discloses an emitter having a pair of electrodes separated by a dielectric. One of the electrodes, a control electrode, defines a hole within which the air (or other gas) will breakdown to produce charged particles. An AC voltage is applied across the electrode pair to form a strong electric field in the hole. In response to the electric field, the air breaks down and charged particles are formed in the hole. A third electrode, a screen electrode, is spaced by a dielectric from the control electrode. A hole in the screen electrode and its underlying dielectric is coaxial with the aperture in the control electrode. The screen electrode is biased with a DC voltage to select certain particle types, e.g., positively charged ions or negatively charged electrons, and accelerate the selected particles toward a substrate. To overcome the tendency of charged particles to diverge as they propagate toward the substrate, Fotland teaches using a deflection electrode to focus the charged particles. As a result, Fotland discloses a complex, multi-layer emitter that is relatively costly to fabricate.
Therefore, a need exists in the art for an inexpensive and simplified plasma discharge emitter device that selectively produces charged particles for patterning a substrate.